Magnetic tunnel junction with perpendicular shape anisotropy and minimised variation of temperature memory point and logic element including the magnetic tunnel junction, method of manufacturing the magnetic tunnel junction

Abstract

A magnetic tunnel junction with out-of-plane magnetisation includes a storage layer; a reference layer; and a tunnel barrier layer. The two magnetisation states of the storage layer are separated by an energy barrier including a contribution due to the shape anisotropy of the storage layer and a contribution of interfacial origin for each interface of the storage layer. The storage layer has a thickness comprised between 0.8 and 8 times a characteristic dimension of a planar section of the tunnel junction. The contribution to the energy barrier due to the shape anisotropy of the storage layer is at least two times greater and preferably at least 4 times greater than the contributions to the energy barrier of interfacial origin.

The invention claimed is: 
     
       1. A magnetic tunnel junction with out-of-plane magnetisation including:
 a storage layer having a magnetisation switchable between two magnetisation states perpendicular to a plane of the layer; 
 a reference layer having a fixed magnetisation and perpendicular to the plane of the layer; 
 a tunnel barrier layer separating the storage layer and the reference layer; 
 
       the two magnetisation states of the storage layer being separated by an energy barrier including a contribution due to the shape anisotropy of the storage layer and a contribution of interfacial origin for each interface of the storage layer, wherein:
 the storage layer has a thickness comprised between 0.8 and 8 times a characteristic dimension of a planar section of the tunnel junction; 
 and the contribution to the energy barrier due to the shape anisotropy of the storage layer is at least two times greater than the contributions to the energy barrier of interfacial origin; 
 
       the storage layer comprising an interfacial layer made of an alloy rich in cobalt in contact with the tunnel barrier. 
     
     
       2. The magnetic tunnel junction according to  claim 1 , wherein the storage layer comprises a volume layer having a Curie temperature above 400° C. 
     
     
       3. The magnetic tunnel junction according to  claim 1 , comprising a single tunnel barrier layer. 
     
     
       4. The magnetic tunnel junction according to  claim 1 , wherein the contribution to the energy barrier due to the shape anisotropy of the storage layer is at least four times greater than the contributions to the energy barrier of interfacial origin. 
     
     
       5. The magnetic tunnel junction according to  claim 1 , wherein the storage layer includes one or more magnetic materials having a Curie temperature above 400° C. 
     
     
       6. The magnetic tunnel junction according to  claim 1 , wherein the storage layer includes an alloy including cobalt and/or iron and an amorphising element, said alloy being in contact with the tunnel barrier layer. 
     
     
       7. The magnetic tunnel junction according to  claim 6 , wherein the storage layer contains one or more layers of materials able to absorb the amorphising element present in the storage layer and to ensure structural transitions between the different magnetic materials comprised in the storage layer. 
     
     
       8. The magnetic tunnel junction according to  claim 1 , wherein its section is circular or quasi-circular and the characteristic dimension is the diameter of the section. 
     
     
       9. The magnetic tunnel junction according to  claim 8 , wherein the diameter is less than 50 nm. 
     
     
       10. The magnetic tunnel junction according to  claim 1 , wherein:
 the tunnel barrier layer is made of MgO, AlOx, AlN, SrTiO 3 , HfOx or any other insulating oxide or nitride; 
 the storage layer includes:
 a layer made of alloy of cobalt, iron and amorphising element of thickness between 1 and 4 nm in contact with the tunnel barrier; 
 a layer of a material able to absorb boron at the moment of post-deposition annealing, of 0.2 to 0.4 nm thickness; 
 a magnetic layer with low Gilbert dampening. 
 
 
     
     
       11. The magnetic tunnel junction according to  claim 1 , wherein:
 said magnetic tunnel junction has a stability factor dependent on the energy barrier and the temperature of use of the magnetic tunnel junction; 
 the composition and the thickness of the storage layer are chosen such that the absolute value of the derivative of the thermal stability factor compared to a characteristic dimension of a planar section of the tunnel junction is less than 10 nm −1 , the derivative of the stability factor being calculated at a temperature T m , the temperature T m  being the average temperature of use of the magnetic tunnel junction. 
 
     
     
       12. A magnetic random access memory point of spin-transfer torque or STT-MRAM type including a magnetic tunnel junction according to  claim 1 . 
     
     
       13. A magnetic random access memory point of spin-orbit transferor SOT-MRAM type including a magnetic tunnel junction according to  claim 1 . 
     
     
       14. A magnetic random access memory point with voltage controlled writing including a magnetic tunnel junction according to  claim 1 . 
     
     
       15. A non-volatile element of a logic component including a magnetic tunnel junction according to  claim 1 . 
     
     
       16. A method for manufacturing a magnetic tunnel junction according to  claim 1  comprising:
 depositing all of the layers by physical vapour deposition; 
 etching the storage layer or thick magnetic layer by reactive ion etching; 
 etching the other layers by ion beam etching. 
 
     
     
       17. The magnetic tunnel junction according to  claim 2 , wherein the Curie temperature is above 800° C. 
     
     
       18. The magnetic tunnel junction according to  claim 5 , wherein the Curie temperature is above 800° C. 
     
     
       19. The magnetic tunnel junction according to  claim 6 , wherein the amorphising element is boron. 
     
     
       20. The magnetic tunnel junction according to  claim 10 , wherein the layer of a material able to absorb boron is a layer of Ta, Mo, W, or Hf.